1. Field of the Invention
This invention relates in general to scanning arrangements for recognizing colors using a scanning device.
2. Description of the Prior Art
A color selection circuit is described in U.S. Pat. No. 3,210,522 in which the desired breakdown of the color recognition space are electronically separated by threshold value circuits for the three color signal values. The output of the threshold value circuits are supplied to a coincidence circuit which produces an output signal of constant amplitude when a color lies within the selected limits of the color recognition space. However, this output signal merely supplies a yes-no decision about the presence of a color in the color recognition space. It is, however, often desired that the output signal provide information about the spatial distance of a color from the center of mass color within the color recognition space.
Color selection circuits for forming correction signals are known from various reproduction techniques which primarily effect the colored corner of the color space (magenta, cyan, yellow, red, blue and green) and all grey values. However, these correction signals do influence large areas in the surface of the color space.
It is, however, important for the selective color correction of skin values that smaller areas of the color space be controlled.
A circuit for the correction for skin values is disclosed in German Pat. No. 1,797,049. In this system, first differential signals are formed by separating the signals into positive and negative primary partial signals and then second differential signals are formed from two of the primary partial signals such that the second differential signals are split into secondary color correction signals according to their plus or minus signs.
A narrowing of the color correction area with the secondary color correction signal by means of correcting the second color signal with the secondary color correction signal to form a third color correction signal is accomplished for obtaining correct skin values. This third color correction signal is, for example, at the maximum the color "light red" and decreases toward zero when the color attains depending on the alteration direction is saturated red, white, magenta and yellow values and all grey values. Thus, this color correction signal for "light red" is still effective in a large area comprising the medium brown shades, light orange and light rose colored mixed values. The large effective range has as a consequence, for example, that the correction signal for a specific light yellowish reddish flesh color tone value lying at the edge of the effective range in the color space is much too small whereas the correction signal for an adjoining color is quite correctly measured. A suitable expansion of the color recognition space would be required for moving these errors which, however, cannot be carried out with the circuit disclosed in German Pat. No. 1,797,049. The color correction area range and the relative signal magnitude distribution in the area space are fixed and are essentially adjusted to the correction of skin or flesh values. A displacement or shifting of the effective range in the color space in order to form a selective correction signal for a random color is not possible so that the circuit cannot be universally utilized. A color selection circuit for obtaining color extraction signals is described in German Auslegeschrift No. 1,512,179.
The color signals produced by scanning a design pattern are supplied amplifiers which have gains which are adjusted such that the output signals of the amplifiers are equal with a freely selected color which is the extraction color. From respectively two output signals differential signals are formed and are connected to one another through a NAND gate. If the selected extraction color is then recognized in the scanned design pattern, the extraction signal will appear at the output of the NAND gate which modulates the luminescence of a writing light for the purpose of recording the color extraction. This circuit also supplies a yes-no statement so that only line extractions but not continuous-tone extractions can be recorded. It is possible indeed, to select a center of mass color, however, means for determining a color recognition space are not provided.
In German Offenlegungschrift No. 2,103,311, an arrangement for reproducing color picture images is disclosed containing a color selection circuit for flesh tones and a corrective network for the production of color correction extraction signals. In this system, comparative voltages of reversed polarity are tapped from a voltage selection circuit and then added to the color signals in the color selection circuit and the comparative voltages are measured such that the three resulting primary differential signals are only then equal with one another if a color signal triple is received at the input of the color selection circuit and the color signal triple corresponds with the flesh tone to be identified. The primary differential signals are simultaneously conveyed to a maximum and a minimum selection circuit through a suitable connection and the selection circuit has an output connected with a differential step device in order to form a secondary differential signal from the largest and smallest primary differential signals. The output signal of the color selection circuit mentioned above is formed by means of superimposition of the secondary differential signal with an adjustable compensation voltage and subsequently reaches the correction network in order to form correction signals.